WO 03/066943 describes the production of a coated polyaramid and the use of this coated polyaramid to produce a reinforced article. A range of matrix materials is given; silicones are among the listed materials. Yarns of poly-p-phenylene terephathalamide (p aramid) are first coated with a curable epoxy compound before application of a second coat of resorcinol-formaldehyde-latex (RFL) and then bonding the double coated polyaramid to a rubber or a rubber like material. The epoxy compound preferably comprises di and/or triglycidyl ether of glycerol or the polyglycidyl ether of polyglycerol. It is stated that the advantage of the invention is that the epoxy pre-coated polyaramid has a good RFL pickup. The use of such a bonding system for silicone rubber has been found to be unsatisfactory due to the unsuitability of RFL as a bonding agent for silicone rubbers. It is desirable to develop a suitable bonding system for silicone rubber because for many high temperature applications, such as turbo hoses for cars, other rubber types are less suitable. Furthermore many reinforcement cords are also unsuited for such high temperature yet low modulus applications. It is therefore an objective to make a strong bond between polyaramid and silicone rubber.
JP4057821 describes a polysulphide modified epoxy resin prepreg composition for polyaramid fibre. The use of this coated polyaramid as a reinforcement for silicone rubber is not disclosed.
JP9124801 describes the coating of polyaramid with polyamide resin in order to improve its bonding to a matrix of epoxy resin.
Organosilanes are well known as bonding agents. Trialkoxyorganosilanes have been used to enhance adhesion of organic polymers to inorganic substrates such as glass and metals. Trialkoxyorganosilanes are hypothesized to promote adhesion though a combination of a coupling mechanism and the formation of interpenetrating networks via hydrolysis of the alkoxy groups to form silanols which then condense to form silsesquioxane networks. Trimethoxysilanes are the preferred trialkoxyorganosilanes for this purpose.
3-methacryloxypropyl-trimethoxysilane is offered by many silane coupling agent manufacturers as suitable for coupling organic materials, such as butyl, polyester, polyether, polyolefin and inorganic materials, such as glass fiber. In U.S. Pat. No. 6,046,262 there is described a dip system comprising a mixture of an aminosilane with another organosilane. In comparative example 5 a 100% polyester fabric sample was dipped into an aqueous dispersion of the organosilane methacryloxypropyltrimethoxysilane and dried. The fabric was then impregnated with resorcinol formaldehyde vinylpyridine latex (RFL) and bonded to SBR. The bond peel strength was shown to be inferior to a sample coated using a dip comprising methacryloxypropyltrimethoxysilane and an aminosilane.
In U.S. Pat. No. 6,096,156 low-pressure plasma treatment of polyaramids to improve their bonding to coatings and rubber is described. A polyaramid cord (Twaron®) is subjected to low pressure plasma treatment including a first plasma stage in which the cord is cleaned by exposure to a plasma containing O2 and CF4 and a second plasma stage in which the cord is plasma coated by exposure to a plasma containing a vinyl compound; such as: acrylic acid, ethylene, butadiene, vinyl pyridine. After this plasma treatment the cord may optionally be further activated by coating with an epoxy compound before it is coated with the usual RFL and bonded to rubber. No mention is made of silicone rubber. It is suggested that the plasma treated polyaramid may have a coating of polysiloxane tackifier applied before bonding it to rubber. This tackifier would be applied over the RFL.
Dow Corning Q-1-6106 adhesion promoter is described in the Material safety data sheet from Dow as being 10 to 30% glycidoxypropyl trimethoxysilane. Dow's product information sheet for Q-1-6106 states that this adhesion promoter will “provide coupling of most reinforcing agents such as glass or Kevlar® to most polar organic polymers and engineering plastics”. Rubbers are not listed among these.